The present invention relates to apparatus and methods for forming the orifice plate for a fluid-jet printing device and particularly to apparatus and methods for assuring planarity of the orifice plate when disposed in an electrolytic bath whereby orifices of uniform size and shape through the orifice plate may be obtained.
In fluid-jet printing technology, a linear array of fluid-jet orifices are formed in a substrate from which filaments of fluid issue to form a plurality of droplet streams for deposition on a substrate. Individually controllable electrostatic charging electrodes are disposed downstream of the orifice plate along the "drop formation" zone. In accordance with known principles of electrostatic conduction, these fluid filaments are provided an electrical charge opposite in polarity and related in magnitude to the electrical charge of the charging electrode. When the droplets separate from the filaments, the induced electrostatic charge is trapped on and in the droplets. The charged droplets then pass through a subsequent electrostatic field and are thereby deflected from a straight downward path toward a catcher structure. Uncharged droplets proceed along the straight path and are deposited upon the receiving substrate.
Recognizing that the size of the individual orifices through the orifice plate is extremely small, a number of different apparatus and methods for forming the orifice plate have been proposed in the past. One such method is disclosed in U.S. Pat. No. 4,528,070, issued July 9, 1985, of common assignee herewith, the disclosure of which is incorporated herein by reference thereto. In that process, a photomask is applied to a stainless steel substrate to form specific images which are resistant to plating in the subsequent nickel-phosphorus plating steps. After the nickel-phosphorus plating is complete, the photomask is removed and the plated stainless steel is exposed to hot ferric chloride, which dissolves the stainless steel in the areas of the photomask not covered by the nickel-phosphorus plating. The resulting apertures through the plated substrate serve as orifices in the orifice plate of a fluid-jet printing apparatus.
To assure that the fluid-jet droplets are formed regularly and precisely, it is important that the orifices formed in the orifice plate be as uniform in size and shape as possible. To achieve this uniformity, it is important that the coating, e.g., the nickel-phosphorus coating, is applied in as uniform and reproducible a manner as possible. In the electroplating process applying the nickel-phosphorus coating, the stainless steel substrate serves as a cathode in the electrolytic bath in which there is also disposed an anode. An electrical potential is applied across the anode/cathode and causes migration of ions to the cathode where they are reduced to nickel and phosphorus. The electrical field which causes the migration should be as uniform as possible across the area of the substrate to assure that the migration takes place uniformly toward the cathode surface. Additionally, the cathode should be as flat or planar as possible in order that the voltage over the surface being plated is as uniform as possible, thus assuring a uniform plating rate.
Uniformity of the electrical field and the voltage over the surface being plated is achieved by making the orifice plate substrate as flat as possible and as parallel as possible relative to a planar anode array. Minor deviations from such planarity and parallelism cause irregularities in the amount of electroplating nickel and phosphorus, resulting in non-uniformity in orifice size and shape. This uniformity has proven somewhat difficult to achieve in practice because the stainless steel orifice plate, which forms the cathode in the electrolytic bath, is quite thin. Also, orifice plates for use in fluid-jet printers for applying ink, chemicals, etc. to textile fabrics are on the order of 1.8 meters long and thus are subject to flexing, bending and twisting, rendering achievement of planarity and parallelism in the electrolytic bath exceedingly difficult.
In accordance with the present invention, there is provided apparatus for assuring the planarity of the orifice plate when in the electrolytic bath. To accomplish this, a tensioning mechanism for placing the cathode/substrate in tension during the electrolytic plating process is provided. Such apparatus includes an elongated frame mounting a pair of arms at opposite ends of the frame spaced one from the other a distance greater than the length of the cathode/substrate. One of the arms is pivoted intermediate its ends to the frame while the other arm is fixed intermediate its ends to the frame. Tension rods and springs extend between corresponding, e.g., upper, ends of the arms. The corresponding opposite, e.g., lower, ends of the arms are provided with a pair of spaced support elements which receive therebetween a pair of jaws for clamping the ends of the substrate. A pair of ceramic, electrical insulating, blocks are disposed between the jaws at each of the ends for grasping an end of the substrate whereby the substrate is electrically insulated from the tensioning mechanism. The jaws also mount a pin which is received in slots formed in the arms such that, when the substrate is tensioned between the arms, uniform tension is applied across the width of the substrate.
Mounted on the frame adjacent the upper end of the pivoted arm is a toggle or over-center lever. The lever may be used to rotate the arm against the bias of the tension spring and thereby locate the lower arm in position to receive the pin. It will be appreciated that, upon release of the lever, the springs bias the arm for rotation in a direction applying tension to the substrate. In this manner, the flatness or planarity of the substrate is assured.
It is important that the tension and hence the flatness and planarity of the substrate be maintained during the electroplating process. To avoid distortion or warpage of the tensioning mechanism when in the bath due to different temperature coefficients of expansion of various materials and to avoid the effects of the corrosive nature of the bath, the arms and the clamps, as well as the frame, are formed of titanium. The springs are formed of a different material, e.g., steel, inasmuch as they are not disposed in the bath.
Prior to inserting the tensioned substrate into the bath, a plurality of electrical connections are spotwelded along the length of the substrate adjacent an edge thereof. The electrical connections are connected to a current control device for regulating current flow along each connection and hence the amount of plating in the immediate area of the substrate about welded electrical connection. That is, the plating is a function of the applied current and the hole size through the orifice plate is a function of the thickness of the plating. The relative thinness of the desired coating is about 6/10 of 1/1000 of an inch and it is desired to control the thickness of the plating to 1% of the thickness. To obtain such high accuracy and resolution, it is necessary to first electrolytically plate a series of substrates and measure the thickness on each substrate in order to ascertain the proper current flow through the electrical connections to the substrate, which, in turn, determines the thickness of the coating applied in the electrolytic bath. Once the proper thickness is obtained, the current controller is set and orifice plates may then be formed. In this manner, consistency, uniformity and reproducibility is achieved and the tensioning mechanism of the present invention contributes to those ends by maintaining the flatness or planarity of the substrate during the electroplating process.
In accordance with a preferred embodiment of the present invention, there is provided apparatus for tensioning an elongated substrate for maintaining planarity thereof during an electroplating process to ensure substantially uniform plating, comprising a pair of means for gripping opposite end portions of the substrate, means connected to one of the gripping means for applying tension to the substrate and means for electrically isolating the tension applying means from the substrate.
In accordance with a further preferred embodiment of the present invention, there is provided an apparatus for tensioning an elongated substrate for maintaining planarity thereof during an electroplating process thereby to ensure substantially uniform plating of the substrate, the apparatus comprising an elongated frame having at least one arm pivotally carried by the frame at one end thereof, a pair of clamps, one of the clamps being carried by the one arm, with the other of the clamps being carried by the frame adjacent the opposite end thereof such that the clamps may grip the opposite ends of the substrate. Means are also provided for electrically isolating the one arm and the frame from the substrate when clamped between the arms, with additional means being carried by the frame for pivoting the one arm in a direction for applying tension to the substrate. Preferably, each clamp includes a pair of jaws between which are carried a pair of insulator blocks for straddling the end of the substrate, the insulator blocks being formed of a ceramic material for electrically insulating the substrate from the frame.
In accordance with a further aspect of the present invention there is provided a method for ensuring the planarity of an elongated substrate during an electroplating process and thereby ensuring substantially uniform plating, including the steps of clamping the opposite ends of a substrate in a frame, applying tension to one end of the clamped substrate to effect planarity thereof between its clamped ends and immersing the frame, while the substrate remains under tension, in an electrolytic bath to plate the substrate.
Accordingly, it is a primary object of the present invention to provide novel and improved apparatus and methods for ensuring the planarity or flatness of a substrate in an electrolytic bath whereby the substrate may form the orifice plate of a fluid-jet printing or applicator device.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.